ADP-ribosylation reactions of proteins can be carried out by specific bacterial toxins, e.g., cholera toxin and E. coli enterotoxin or by enzymes in a variety of tissues and organs. Our interest is to study the process in skeletal muscle, because we found activities present in this tissue that carry out ADP- ribosylation and de-ADP ribosylation reactions consistent with a regulatory function for these reactions. We have purified these enzymes and propose to use these enzymes to delineate the role(s) of these enzymatic reactions in skeletal muscle. We will examine, e.g., Ca+2 regulated processes, protein phosphorylation and evaluate the molecular basis of these types of reactions. Specifically we plan to study the following topics: I. ADP-ribosylation and de ADP-ribosylation in skeletal muscle A. Studies in membranes B. Studies with exogenous protein substrates 1. Phosphorylase kinase 2. Glycogen phosphorylase II. Properties of ADP-ribosyltransferase the hydrolase A. Kinetic studies B. Chemical characterization III. Chemical aspects of mono ADP-ribosylation and factors influencing the specificity of the enzymatic reactions A. Specificity B. Affinity HPLC C. Active site reagents - ADP-ribosylation